Installation stops early and PHP 5 is required is in the Title

I know this subject's been discussed a few times before, but it seems my case is a little different, hence the new discussion line...

I'm trying to install SS 2.3 on a public server. The first part goes fine (SS is not complaining about anything) and then when I start the installation, it stops after 4 lines (attached screenshot) and the page title reads "PHP 5 is required". After going through the posts here on the forum I tried the following:
- called phpinfo(); to check if php5 was running - it was
- I asked the server admin to change read/write rights to all files in the folder (especially .htaccess and the config file) so the server could modify them,
- I created 'temp', 'tmp' and 'silverstripe-cache' folders in the root folder and did the above to them
- I added

to my .htaccess file, which ended with about 500 lines of strange-looking code being printed but still didn't help (screenshot 2).
- took backup of local working SS database and restored it on server

I'm wondering if my case is not similar to this one: I finally got them to look at the .htaccess rewrite requirements for SilverStripe and they admitted that their system only allows simple .htaccess commands.

Why? First of all, after putting the 'fresh' SS installation package in my root folder, going to my www.mysite.com produced an empty/white page. To start the installer, I had to go to www.mysite.com/install.php, which seems to me like some re-write problems perhaps.

I will check with my server admin if he can check the .htaccess file and perhaps the problem is there.

But still I would be grateful for any more tips and advice on how to get my SS up and running.